idle spark fluctuation

[_scorpion_]

hi

the subject is jeep 6.4 my2014, forged, supercharged, etc.
i'm ok about my current tune, it runs fine, no issue.

one thing does not let me calm down - spark at idle jumps here and there, 3 to 22 - i attach a small lot.
i assume this is not really normal and needs to be settled.

any advice/ideas on that please?

[rays04gtx]

hi

the subject is jeep 6.4 my2014, forged, supercharged, etc.
i'm ok about my current tune, it runs fine, no issue.

one thing does not let me calm down - spark at idle jumps here and there, 3 to 22 - i attach a small lot.
i assume this is not really normal and needs to be settled.

any advice/ideas on that please?

your PT/MBT/Min Spark tables, narrow them up. your spark tables as they are now allow up to 42* swing , your rpm error is a total or 40*, and your engine wants to swing 17*

1st attachment is what you currently have(PCM52)
2nd attachment is where I would have those cells on those tables(the rest of the table would be modified to match area, but for demonstration I only changed the targeted cells being used), now if it surges at the values I choose , I would up the MBT table were I have 13.5* I would up it to 16* and smooth area accordingly.

3rd attachment are graphs focused on the RPM area and Aircharge of the log sample. 1st panel is avg, 2nd is max and 3rd is Min, you can see from the avg panel it wants to idle at 11.2* , TAF is relatively steady at 11.5 G/s so it's not an Air issue , tune looks great other wise.......Might want to raise Desired Idle to 750ish , What cam is in it? more interest in Duration and Centerline, I don't care about lift in this situation.

[_scorpion_]

hi rays04gtx
thanks for the input, I shall definitely try that.
unfortunately I have no details which cam it is and no way to find out. the only thing I know is that it is non-mds one, with very little difference comparing to the stock

[_scorpion_]

your PT/MBT/Min Spark tables, narrow them up. your spark tables as they are now allow up to 42* swing , your rpm error is a total or 40*, and your engine wants to swing 17*

1st attachment is what you currently have(PCM52)
2nd attachment is where I would have those cells on those tables(the rest of the table would be modified to match area, but for demonstration I only changed the targeted cells being used), now if it surges at the values I choose , I would up the MBT table were I have 13.5* I would up it to 16* and smooth area accordingly.

3rd attachment are graphs focused on the RPM area and Aircharge of the log sample. 1st panel is avg, 2nd is max and 3rd is Min, you can see from the avg panel it wants to idle at 11.2* , TAF is relatively steady at 11.5 G/s so it's not an Air issue , tune looks great other wise.......Might want to raise Desired Idle to 750ish , What cam is in it? more interest in Duration and Centerline, I don't care about lift in this situation.

hi again
finally got some spare tome today to play around.
I did what you suggested; the test with 0min-11pt-13mbt was success, so I went further and finished with 2min-10pt-16mbt in the idle area. I idles smoother, no jerk feeling.
What is bothering me is that this way we basically limit the pcm within narrow borders; but why is it trying to increase/decrease the spark? don't we fix the symptoms without curing the root cause?

anyway thanks for the idea, it feel much better indeed.

[PurpleRam]

Best way to describe this is, your super charger is the root cause, have you been to a cruise night were there’s an old school blower car, you’ll notice they surge a lot, it’s because of a lean/rich cycle, when it’s rich it lowers idle, lean it raise , with modern electronics we have tighter control over fuel/air/spark., the tighter we we can make the parameters the smoother the idle……with in reason,

So root cause is the nature of the beast known as blower surge

[PurpleRam]

Let me get a little deeper , the idle wants to fluctuate because of vacuum signal, the more vacuum the more air/fuel is drawn into the cylinder, back in the day our distributor held a steady (hopefully) value, let us say 10* , now the carb idle screws set a fixed amount of fuel that can be drawn into the cylinder, only variable is air, more air drawn in, the leaner, idle raises sine the volume is a fix amount, the next cylinder gets less air but same fuel, idle lowers,Blower cars force more air fuel, same principle just more exaggerated. Now modern electronics we don’t have a set “distributor “ value we have a variable table, but we have strict fuel and air controls now, there’s more but my flight is being called

[dodgeboy]

I have seen tuners do that to imitate a lopey idle. Mine idles smooth even with a 274 Comp cams cam and Whipple.
My tuner (OST Dyno) did a great job on mine for driveability and power combination. I just want a little more aggressive throttle in sport mode.

https://www.youtube.com/watch?v=drJ3srCVn7U

[LilSick]

rick is talking about airflow

mechanically forced air

that reckless guy is about faking something else

[_scorpion_]

Something of that kind was in my head but you structured that. So the theory is understood. Not, that being said, in my (and seems not only mine) practical case - is limiting the spark to a "comfortable feeling" the only way to go? or there's something else, like playing with torque/speed density/anything?

[PurpleRam]

Something of that kind was in my head but you structured that. So the theory is understood. Not, that being said, in my (and seems not only mine) practical case - is limiting the spark to a "comfortable feeling" the only way to go? or there's something else, like playing with torque/speed density/anything?

Yes(ish) , it can be done , but it's More complex and time consuming, and the end result is not as precise. Speed density= Carb Idle screws(at these rpms) and we can fine tune Idle with it, but if the VE difference between total and base is 0 or with in +/- 1 it's not worth the time involved, as for Torque/Friction, if the car lurches off Idle and it's not solved with Spark/Ve then yes we would look in to it.

Spark is the best way to deal with it with Modern Electronics, once the automotive world discovered(improved) Crank trigger spark, it increased the engines' ability to be more efficient, but because of the nature of the internal combustion engine , it wonders around when not limited to set parameters , 30(40) years ago those parameters were mechanical , now there are digital.

[PurpleRam]

I have seen tuners do that to imitate a lopey idle. Mine idles smooth even with a 274 Comp cams cam and Whipple.
My tuner (OST Dyno) did a great job on mine for driveability and power combination. I just want a little more aggressive throttle in sport mode.

https://www.youtube.com/watch?v=drJ3srCVn7U

if you want it to sound like a prostocker that can't idle and burn up a f'ton of fuel at idle......yes follow RECKLESSmotors advice........Chopy idle is easy to achieve if you want that , but like so many things there's a trade off, like you said Mike at OST(one of the GREATEST at BOOST TUNING) has your car idling SMOOTH with a 274 and a Whipple .

[_scorpion_]

Yes(ish) , it can be done , but it's More complex and time consuming, and the end result is not as precise. Speed density= Carb Idle screws(at these rpms) and we can fine tune Idle with it, but if the VE difference between total and base is 0 or with in +/- 1 it's not worth the time involved, as for Torque/Friction, if the car lurches off Idle and it's not solved with Spark/Ve then yes we would look in to it.

Spark is the best way to deal with it with Modern Electronics, once the automotive world discovered(improved) Crank trigger spark, it increased the engines' ability to be more efficient, but because of the nature of the internal combustion engine , it wonders around when not limited to set parameters , 30(40) years ago those parameters were mechanical , now there are digital.

got that sir! thanks so much for involvement

[LilSick]

if you want it to sound like a prostocker that can't idle and burn up a f'ton of fuel at idle......yes follow RECKLESSmotors advice........Chopy idle is easy to achieve if you want that , but like so many things there's a trade off, like you said Mike at OST(one of the GREATEST at BOOST TUNING) has your car idling SMOOTH with a 274 and a Whipple .

it was actually idling a little bit high and was stalling but ok

any idea why mike woulda set it up to run on default mode and not sport?

is there a logic to that when boosted with that cam?

i mean it runs in both but the owner sees no difference

[PurpleRam]

it was actually idling a little bit high and was stalling but ok

any idea why mike woulda set it up to run on default mode and not sport?

is there a logic to that when boosted with that cam?

i mean it runs in both but the owner sees no difference

I don’t know, he’s usually has good reason for what he does, also owner might of said something that lead Mike to think only one mode was needed, has the car always stumbled? I harp on this a lot, if the car/truck all of a sudden changes how it acts, disconnect the battery and reload the tune it’s not always the cure, but it eliminates the chance the ecu adapted to the tune. …. These GPEC ecu are more adaptive than people think

[GeForce1986]

great subject to read

[dodgeboy]

no, I am not doing a chop chop idle tune. I just said I heard of people messing with timing to imitate cam overlap. I think that is stupid. Pulled fuse, reset adaptive runs fine.